interface A {
    double f (double x,double y);
}
class B implements A {
    public double f(double x,double y) {
        return x*y;
    }
    int g(int a,int b) {
        return a+b;
    }
}
public class E6_1 {
public static void main(String args[]) {
    A a = new B();
    System.out.println(a.f(3,5));
    B b = (B)a;
    System.out.println(b.g(3,5));
  }
}
